Fallout 3 was released in 2008. In that time, all kinds of gorgeous video games have come and gone, including Bethesda's own Skyrim. But you wouldn't tell by looking at these screens. You'd think they were for Fallout 4, a thing I'm pretty sure doesn't even exist yet.
That's the power, and the beauty, of mods for you. In this case, the famous ENB Series tweak, which along with hi-res landscape textures, improved faces and some changes made to the game's lighting have Fallout 3 looking better than ever (you can get links for some of those used in the comments here).
It also helps that the guy taking the shots, Anthemios / trillville, knows how to take a very pretty picture.
You can check out nice, hi-res versions of the images at the link below. Which you definitely should. Especially if give half a damn about desktop wallpaper.